A preheater involves the use of condensing steam at 100°C on the inside of a bank of tubes to heat air that enters at 1 atmosphere and 15°C. The air moves at 8 m/s in cross flow over the tubes. Each tube is 2 m long and has an outside diameter of 5 mm. The bank consists of 196 tubes in a square, aligned array in which the distance between tube centers is 15 mm. What is the temperature of the air after passing through the tubes. Also, what is the pressure drop associated with the air flow?

A preheater involves the use of condensing steam at 100°C on the inside of a bank of tubes to heat air that enters at 1 atmosphere and 15°C. The air moves at 8 m/s in cross flow over the tubes. Each tube is 2 m long and has an outside diameter of 5 mm. The bank consists of 196 tubes in a square, aligned array in which the distance between tube centers is 15 mm. What is the temperature of the air after passing through the tubes. Also, what is the pressure drop associated with the air flow?

Principles of Heat Transfer (Activate Learning with these NEW titles from Engineering!)

8th Edition

ISBN:9781305387102

Author:Kreith, Frank; Manglik, Raj M.

Publisher:Kreith, Frank; Manglik, Raj M.

Chapter6: Forced Convection Over Exterior Surfaces

Section: Chapter Questions

Problem 6.38P

See similar textbooks

Similar questions

Countercurrent Water-Cooling Tower. A forced-draft countercurrent water-cooling tower is to cool water from 43.3 to 26.7°C. The air enters the bottom of the tower at 23.9°C with a wet bulb temperature of 21.1°C. The value of Hg for the flow conditions is Ho = 0.533 m. The heat-transfer resistance in the liquid phase will be neglected; i.e., h, is very large. Hence, values of H* should be used. Calculate the tower height needed if 1.5 times the minimum air rate is used.
A heat recovery device involves transferring energy from the hot flue gases passing through an annular region to pressurized water flowing through the inner tube of the annulus. The inner tube has inner and outer diameters of 24 and 30 mm and is connected by 8 struts to an insulated outer tube of 80-mm diameter. Each strut is 3 mm thick and is integrally fabricated with the inner tube from carbon steel (k= 50 W/m·K). Consider conditions for which water at 300 K flows through the inner tube at 0.161 kg/s while flue gases at 800 K flow through the annulus, maintaining a convection coefficient of 100 W/m2·K on both the struts and the outer surface of the inner tube. What is the rate of heat transfer per unit length of tube from gas to the water? Use the Dittus-Boelter equation to obtain the water-side convection coefficient. - Determine the rate of heat transfer per unit length of tube from gas to the water, in W/m.
The evaporator section of a heat pump is installed in a large tank of water, which is used as a heat source during the winter. As energy is extracted from the water, it begins to freeze, creating an ice/water bath at 0°C, which may be used for air conditioning during the summer. Consider summer cooling conditions for which air is passed through an array of copper tubes, each of inside diameter D = 59 mm, submerged in the bath. (a) If air enters each tube at a mean temperature of Tm,i = 25°C and a flow rate of m·=0.01 kg/s, what tube length L is needed to provide an exit temperature of Tm,o = 16°C? With 10 tubes passing through a tank of total volume V = 11 m3, which initially contains 83% ice by volume, how long would it take to completely melt the ice? The density and latent heat of fusion of ice are 933 kg/m3 and hsf = 3.34 × 10^5 J/kg, respectively.
Air at a pressure of 101.3 kPa and 288.8 K enters inside a tube having an inside diameter of 12.7 mm and a length of 1.52 m with a velocity of 24.4 m/s. Condensing steam on the outside of the tube maintains the inside wall temperature at 372.1 K. Calculate the convection coefficient of the air. (Note: This solution is trial and error. First assume an outlet temperature of the air.)
Question No.15: a) Derive an expression for turbulent boundary layer thickness over a flat plate. b) The flow rates of hot and cold water streams running through a parallel flow heat exchanger are 0.2 kg/s and 0.5 kg/s respectively. The inlet temperatures on the hot and cold sides are 75°C and 25°C respectively. The exit temperature of hot water is 45°C. If the individual heat transfer coefficients on both sides are 650 W/m°C, calculate the area of the heat exchanger.
Heating Air by Condensing Steam. Air at a pressure of 101.3 kPa and 288.8 K enters inside a tube having an inside diameter of 12.7 mm and a length of 1.52 m with a velocity of 24.4 m/s. Condensing steam on the outside of the tube maintains the inside wall temperature at 372.1 K. Calculate the convection coefficient of the air. (Note : This solution is trial and error. First assume an outlet temperature of the air.)
A non-thermally insulated industrial water vapor pipe is 25 m long and 100 mm in diameter. This line crosses a building whose walls and ambient air are at 25oC. Pressurized steam holds the tube surface at 150oC and the convective coefficient is 10 W/(m.K). The surface emissivity is ε=0.8. (a) the heat loss on this line; (b) if the steam is generated in a boiler that operates at 90% efficiency and uses natural gas priced at $0.20/MJ, what is the annual cost of this heat loss? Answer: (a) 18.41 W; (b) $129,000
The condenser of a steam power plant consists of AISI 302 Stainless steel tubes, each with outer and inner diameters of 35 mm and 30 mm, respectively. Saturated steam at 0.135 bar condenses on the outer surface of the tube, while water at a mean temperature of 295 K is in fully developed flow through the tube (you can assume that 295 K is the mean temperature in the axial direction of the tube (e.g. along its length) or you may assume that the inlet water temperature is 295 K). For a water mass flow rate of 0.22 kg/s, what is the outer surface temperature of the tube and the rates of heat transfer and steam condensation per unit tube length? As an approximation you may evaluate the properties of the liquid film at the saturation temperature.
Air with an average temperature of 25oC flows inside a tube arrangement consisting 10 rows of tubes. Each tube has an outer diameter of 1.9 cm. The air enters the tube arrangement inlet at 2 m/s velocity. Calculate the heat transfer coefficient, coefficient of friction, and pressure drop inside the tube arrangement if: a) Using staggered tube arrangement with b) Using aligned tube arrangement with
Ethylene glycol with a mass flow rate of 0.01 kg / sec flows in a thin-walled pipe with a diameter of 3 mm. The pipe is in the form of a serpentine, and was lifted into a well-mixed water bath at 25 ° C. Calculate the heat transfer and pipe length required for the fluid to enter the pipe at 85 ° C and exit at 35 ° C?
6) In a boiler installation coal is burnt at the rate of 1.9 x 10³ kg/hr and hot gases are generated at the rate of 18 kg per kg of coal burnt. Hot gases are at the temperature of 600 K and ambient air temperature is 300 K Different pressure losses in furnace grate, flues, bends and chimney are measured to be 6 mm, 5 mm, 3 mm, and 1 mm of water respectively. Hot gases leaving chimney have velocity equivalent to 1.2 mm of water column. Considering the actual natural draught to be 80% of theoretical draught determine the height and diameter of chimney.
An air duct heater with an electric heating element in an industrial plant is used. 12 m/s velocity perpendicular to the elements from above to the atmospheric air heater and enters at 27 oC. In the duct heater, each row consists of 3 pipes in the flow direction. It consists of 4 rows. In this air duct heater any two pipes The distance between the centers is 22 mm. Each element in the heater is 12 mm outside diameter, 220 mm length and a uniform surface temperature of 330 oC. Air duct Find the heat transfer rate in the heater and the temperature of the air leaving the heater.